This disclosure is generally related to wireless communications technologies, including fourth generation (“4G”) Worldwide Interoperability for Microwave Access (“WiMAX”) and/or Long-Term Evolution (LTE) technologies. In one or more embodiments, this disclosure is directed to a system and method for controlling uplink (UL) power of a mobile station (MS) in a Radio Access Network (RAN), such as a WiMAX RAN, or user equipment (UE) in an LTE network. In one or more embodiments, this disclosure is useful for allowing a base station (BS) of a WiMAX RAN or an eNodeB (eNB) of an LTE RAN to perform MS or UE UL power control so that unnecessary packet losses and high UL signal level and interference can be avoided, and so battery power in the MS or UE can be conserved.
International Mobile Telecommunications-Advanced (IMT Advanced), better known as “4G”, “4th Generation”, or “Beyond 3G”, is the next technological strategy in the field of wireless communications. A 4G system may upgrade existing communication networks and is expected to provide a comprehensive and secure IP based solution where facilities such as voice, data and streamed multimedia will be provided to users on an “anytime, anywhere” basis, and at much higher data rates compared to previous generations. 4G devices provide higher speed and increased Quality of Service (“QoS”) than their third generation or “3G” counterpart devices. WiMAX and LTE devices and networks are examples of “4G” technologies.
Quality of Service is determined by various factors, including variable signal conditions on the wireless link; throughput, latency/delay and transmission errors which vary much more widely over a wireless connection because of the constantly changing radio signal conditions and extensive digital radio processing. Standard internet protocols, designed for use over a more stable wire-based connection, are not well-suited to handle these variations.
Admission control is performed by the BS during network entry and re-entry for statically-provisioned service flows (SF), e.g. initial service flows, and is also performed by the BS in response to dynamic BS-initiated or MS-initiated requests to create service flows. Further, Admission control is performed by the BS during handovers. Admission control can be used to limit the amount of total air interface resources that are consumed by real-time service flows. Since real-time service flows are allocated resources before non-real-time and best effort service flows, this feature prevents real-time traffic from “starving” best effort traffic.
A fundamental feature of WiMAX involves the classification of traffic into separate service flows. Different QoS attributes can be defined for each SF based on the type of traffic. To support multimedia applications, the WiMAX standard defines five types of data delivery service flows for downlink (DL) flows, and five corresponding scheduling services for uplink (UL) flows: UGS—Unsolicited Grant Service, with constant bit-rate services (CBR); rtPS—Real Time Polling Service, with variable bit-rate, but sensitive to delay; ertPS—Extended Real Time Polling Service, for VoIP; nrtPS—Non-real Time Polling Service, time insensitive, but require a minimum bandwidth allocation; and BE—Best Effort. Uplink is differentiated from downlink because uplink flows (except UGS) involve some form of request/grant mechanism for resource allocations. The order of priority given to services while transmitting is generally as follows: UGS>ertPS>rtPS>nrtPS>BE. However, the particular scheduling mechanism is generally left to proprietary implementations.
In the UL direction, all SF types except UGS involve some form of bandwidth request/grant mechanism for bandwidth allocation. In the DL, the BS scheduler has all the information about DL SF status for making the best scheduling decision. However, UL SF status information is distributed in the MSs. Additionally, an MS may need to be assigned some small bandwidth to send UL SF status information to the BS. Therefore, some mechanisms (e.g., “Bandwidth Request Header” [BRH] or “Bandwidth Request and UL Tx Power Report Header” [BRTH]) are required to inform the BS scheduler of UL SF status (i.e., BRH or BRTH messages). Basically, BR refers to a mechanism MSs use to indicate to the BS their bandwidth needs, and BRTH refers to a similar mechanism in which MSs indicate not only their bandwidth needs to the BS, but which also provide an indication of UL transmit (Tx) power.
LTE is the project name of a high performance air interface for cellular mobile communication systems and is a step toward 4G radio technologies designed to increase the capacity and speed of mobile telephone networks. Where the current generation of mobile telecommunication networks are collectively known as 3G, LTE is marketed as 4G. Most major mobile carriers in the United States and several worldwide carriers announced plans to convert their networks to LTE beginning in 2009. LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) which is introduced in 3rd Generation Partnership Project (3GPP) Release 8, with further enhancements in Release 9. These enhancements focus on adopting 4G mobile communications technology, including an all-IP flat networking architecture.
The QoS levels provided in the LTE evolved packet system (EPS) relies upon the concept of a “bearer”, which is a packet flow established between the packet data network gateway (PDN-GW) and the user equipment, UE. The traffic running between a particular client application and a service can be differentiated into separate service data flows (SDFs). SDFs mapped to the same bearer receive a common QoS treatment (e.g., scheduling policy, queue management policy, rate shaping policy, radio link control (RLC) configuration). A bearer is assigned a scalar value referred to as a QoS class identifier (QCI), which specifies the class to which the bearer belongs. QCI refers to a set of packet forwarding treatments (e.g., scheduling weights, admission thresholds, queue management thresholds, and link layer protocol configuration) preconfigured by the operator for each network element. The class-based method improves the scalability of the LTE QoS framework. Bearer management and control in LTE follows the network-initiated QoS control paradigm, and the network initiated establishment, modification, and deletion of the bearers.
Similar to WiMAX service flows, LTE offers two types of bearers, i.e., (1) Guaranteed bit rate (GBR), in which dedicated network resources related to a GBR value associated with the bearer are permanently allocated when a bearer becomes established or modified; and (2) Non-guaranteed bit rate (non-GBR), in which a non-GBR bearer may experience congestion-related packet loss. A non-GBR bearer is referred to as the default bearer, which is also used to establish IP connectivity, similar to the initial SF in WiMAX. Any additional bearer(s) is referred to as a dedicated bearer, and can be GBR or non-GBR. Maximum bit rate (MBR) is the maximum sustained traffic rate the bearer may not exceed, and is only valid for GBR bearers. The GBR represents the minimum reserved traffic rate the network guarantees, and is only valid for GBR bearers.
As may be seen from the above, WiMAX and LTE have many similar features. For example, WiMAX utilizes CQI, throughput, CINR, and MIMO that are all present in LTE. QoS is also similar between WiMAX and LTE. LTE employs dedicated bearers similar to service flows in WiMAX. Admission control is applied for GBR bearers in LTE similar to WiMAX. LTE bearers can be configured for semi-persistent scheduling similar to unsolicited grants for UGS and ertps service flows in WiMAX. Both LTE and WiMAX provide mechanisms to suspend and resume semi-persistent/unsolicited grant resource allocations.
In WiMAX, a BS uses radio-frequency (RF) signals to connect MSs, and the BS is in charge of network functionality. Data transmitted by MSs will go through the BS and the operator backbone network before reaching the Internet. When a MS wants to transmit data, one channel access method in the IEEE 802.16 standard uses a code division multiple access (CDMA) method. The CDMA ranging method selects between many different CDMA ranging codes in a CDMA code group. Upon a successful CDMA code reception, the MS is granted bandwidth to send a request for bandwidth (BRH or BRTH) to the BS for reserving future bandwidth.
The IEEE 802.16 standard defines four CDMA code groups for the use of the CDMA ranging method, i.e., Initial Ranging, Periodic Ranging, Handover Ranging (HO), and BR. When the MS wants to send a BR, it randomly chooses a ranging code in the BR ranging code group and then sends the ranging code to the BS. Once the BS receives the ranging code from the MS, it reserves bandwidth in later frames for the MS. This CDMA method can have the benefit of avoiding a collision under the assumption that different MSs choose different ranging codes when they simultaneously send BRs to the BS. Under some circumstances, this CDMA ranging method can greatly improve the BR transmission success rate, but it is possible for identical CDMA ranging codes to be selected by different MSs and to be sent in the same ranging slots.
FIG. 1 illustrates a conventional call flow or message procedure for contention based bandwidth request (BR) under the existing WiMAX standard in which the MS sends a CDMA ranging code (CDMA code) to the BS. In response to this “best case” scenario, the BS sends an allocation information element (IE) to the MS, which then requests bandwidth by means of the BRH message. The BS assigns an UL bandwidth (BW) allocation to the MS. After BW is allocated, the MS may then transmit data to the BS via UL protocol data units (PDU).
However, the current WiMAX standard often leads to unnecessarily high UL signal power and interference, and short mobile device battery life. In the current WiMAX standard, the BS will not respond to the MS if it cannot decode the CDMA ranging code, either due to insufficient UL power, or a packet collision by two MSs transmitting the same CDMA ranging code in the same ranging slots. Further, the MS will increase its power and sends another BR CDMA code when it does not receive any response from the BS for the previous CDMA code,
The current WiMAX standard does not include triggers for the MS to adjust its transmit power after this CDMA ranging procedure for the following data transmissions to allow the MS to operate at an appropriate power level to conserve precious mobile device battery power. In a typical case, when the failure of ranging codes is due to collisions, the conventional approach leads to unnecessarily high MS transmit power and high UL signal level and interference between BR ranging codes and the next power adjustment.
FIG. 2A illustrates a conventional packet collision scenario (from the MS perspective) that is possible under the existing WiMAX standard and in which sustained power boosting is used, but is unnecessary. FIG. 2B illustrates the associated call flow or message procedure between MS and BS related to FIG. 2A. Lost CDMA ranging codes occur before time t, and power boosting is applied at time t but is not necessary. FIG. 2B shows three CDMA codes being sent, where the first two were unable to be decoded by the BS. Once the third CDMA code is received and decoded, the BS sends an allocation IE to the MS, a BRH message is sent at the successful power level (i.e., P+2d), and an UL BW allocation is sent to grant bandwidth to the MS by the BS. Normal UL PDU communication then occurs at the P+2d power level. WiMAX typically uses power increments of 3 dB for each CDMA code re-transmission.
FIGS. 2A and 2B illustrate the wasting or the unnecessary boosting of MS power, at least after the initial CDMA ranging is resolved. Extended power boosting in this scenario can lead to high interference, an unnecessarily high UL signal power level, and short MS device battery life.
FIG. 3A illustrates a different conventional power shortage scenario (from the MS perspective) in which sustained power boosting is not maintained, and in which packets may be lost. FIG. 3B illustrates a previously proposed WiMAX standard change that provides a call or message flow procedure between MS and BS related to the power shortage scenario of FIG. 3A. This prior art solution to the problem with the existing WiMAX standard attempts to apply a UL power increase only until the first UL allocation after the CDMA ranging procedure. Thereafter, packet losses may occur before the next UL power adjustment. In FIG. 3A, power boosting is applied at time t after the MS CDMA ranging code has been unsuccessfully received and/or decoded by the BS. However, in this prior art implementation, rather than maintain the boosted UL power, at time (t+n) the UL power is reduced after receiving a BW allocation. The call flow diagram of FIG. 3B shows that UL power is initially boosted until the first UL allocation assigned by the allocation IE to the MS by the BS, resulting in potential for UL PDU packet losses due to insufficient MS UL transmit power.
The WiMAX OFDMA system applies CDMA ranging for initial ranging, periodic ranging, handover (HO) ranging, and bandwidth request (BR) ranging. When a MS sends a CDMA code but fails to receive a response, there are two possible causes, as the above scenarios illustrate:
(1) A collision scenario results when multiple MSs using the same CDMA ranging code in the same ranging slots may result in boosted MS power being maintained on other bursts as well as future BR code and BRH until a new power correction occurs. However, boosted power may not be needed as the power boosting results from collisions of CDMA codes from different MSs, and not by a power shortage. Too much power boosting leads to high interference, unnecessarily high UL signal power level, and short mobile device battery life.
(2) A power shortage scenario may occur when boosted MS power is not applied on other bursts. However, these bursts may need boosted power if a previous BR code failure is due to insufficient transmit power. In this case, it is necessary for the MS to increase its transmission power. However, typically the MS is unable to tell if the failure is due to packet collision or insufficient MS transmission power.
The current WiMAX standard essentially only solves the problem of insufficient MS transmission power (see FIGS. 2A and 2B). Specifically, the current standard supports an passive open loop MS power control mode, where the power per a subcarrier is specified as being required to be maintained for the UL transmission as in equation (1), below:P(dBm)=L+C/N+NI−10 log 10(R)+Offset—SSperSS+Offset_BSperSS  (1)where IEEE 802.16-2009 defines these terms as follows:P is the Tx power level (dBm) per a subcarrier for the current transmission, including MS Tx antenna gain;L is the estimated average current UL propagation loss, and shall include MS Tx gain and path loss, but exclude the BS Rx antenna gain;C/N is the normalized carrier-to-noise ratio of the modulation/forward error correction (FEC) rate for the current transmission;R is the number of repetitions for the modulation/FEC rate;NI is the estimated average power level (dBm) of the noise and interference per a subcarrier at BS, not including BS Rx antenna gain;Offset_SSperSS is the correction term for SS-specific power offset, and is controlled by the MS, with an initial value of zero;Offset_BSperSS is the correction term for SS-specific power offset, and is controlled by the BS with power control messages.
As in FIGS. 2A and 2B, when a MS sends CDMA codes for BR, if the MS does not receive a response, the MS sends a new CDMA code at the next appropriate opportunity at one step higher power level, e.g., increasing in +3 dB increments, up to a predefined maximum power value. In addition, the power increase during the CDMA code re-transmission procedure is reflected into the term “Offset_BSperSS” in the above power control formula. That is, the power increase is applied to all future UL transmissions.
While it may be appropriate to apply such open loop power increases to future UL allocations when the failure in receiving a response is due to insufficient UL transmission power, this could cause problems when the failure is due to collisions, such as an unnecessarily high UL signal power level. In addition, this also leads to high interference level and short MS battery life.
In recognition of the above issues, the proposed WiMAX solution illustrated in FIGS. 3A and 3B considers the case of packet collision and proposes that the MS shall not increase “Offset_BSperSS” or “Offset_MSperSS” based on CDMA ranging success or failure. Further, when the MS performs a BW Request CDMA ranging retry or Periodic CDMA ranging retry and increases MS transmit power, the MS shall apply the same increase in transmit power to future CDMA ranging attempts until a response is received from the BS, e.g., either a RNG-RSP or CDMA allocation IE. After a response is received, future CDMA ranging attempts shall not use this transmit power increase. Finally, when the MS performs a BW Request CDMA ranging “retry” and increases MS transmit power, the MS shall apply the same increase in transmit power to the UL allocation provided by the CDMA allocation IE. The transmitted power of other bursts will not be affected from this amount of power adjustment.
FIG. 3A illustrates proposed power shortage solution scenario (from the MS perspective) possible under the existing WiMAX standard in which sustained power boosting is not maintained, and in which packets may be lost. FIG. 3B illustrates a previously proposed change to the WiMAX standard that provides a call or message flow procedure between MS and BS related to the power shortage scenario of FIG. 3A. This proposed, but not yet implemented “solution” to the problem with the existing WiMAX standard attempts to apply a UL power increase only until the first UL allocation IE is received. Thereafter, packet losses may occur before the next UL power allocation. In FIG. 3A, power boosting is applied at time t, after the MS CDMA ranging code has been unsuccessfully received and/or decoded by the BS. However, in this proposed implementation, rather than maintain the boosted UL power, at time (t+n) the UL power is reduced after receiving a BW allocation. The call flow diagram of FIG. 3B shows that UL power is initially boosted only until an allocation IE is sent to the MS by the BS, resulting in potential for UL PDU packet losses due to insufficient MS UL transmit power for subsequent packets.
Essentially, this proposed, but not yet implemented approach removes the power increases during the ranging procedure from future UL transmissions, except for the UL allocation provided by the CDMA allocation IE immediately after a BR ranging.
While this proposed approach does solve the issues of the current WiMAX standard as indicated above, in the case when the power increase is due to insufficient transmission power, which is a typical case, this approach makes the MS operate at insufficient power levels until the next power control adjustment cycle, and hence often leads to packet losses between the removal time of the power increases and the next power control adjustment from the BS.
LTE encounters similar problems in establishing the required bandwidth for a number of mobile users who may either be “colliding” with each other, or who may have insufficient UL transmit power.
Further, and although the current WiMAX standard does allow the BS to control the MS UL power in a closed loop manner, the existing algorithm used does not account for MS UL power as an input to the closed loop power control algorithm.
What is needed is a system and method of wireless communications that improves connectivity for mobile users, and which accounts for different mechanisms that may inefficiently boost MS UL power. What is further needed is a system and method for wireless communications that provides improved UL power management, including the ability to selectively allow the BS to provide MS UL power control to improve QoS and conserve MS battery power.